1. Field of the Invention
The present invention relates to a magnetic recording medium which is prepared by forming a magnetic layer on a substrate by coating a magnetic powder composition comprising a magnetic powder and a binder as main components. More particularly, it relates to a magnetic recording medium having excellent repeat running durability and excellent output variation which is suitable for an audio tape and a video tape.
2. Description of the Prior Art
In general, a magnetic recording medium is prepared by coating a magnetic powder composition of a magnetic powder and a binder on a support such as a film made of polyacetate, polyvinyl chloride, polyester etc.
Various kinds of the binder have been proposed to use in the magnetic powder composition. However, a magnetic recording medium having both satisfactory characteristics of the output variation and the repeat running durability has not been found.
The typical binders which have been used in the conventional magnetic recording medium, are combinations of an urethane resin, a vinyl chloride-vinyl acetate copolymer, a cellulose resin, an epoxy resin or a phenoxy resin. Both the characteristics could not be satisfied by the conventional combinations of the resins. The thermoplastic resins have been mainly used as the binder of the combination. Thus, the preparation and the handling of the magnetic powder composition have been advantageously simple. However, when the magnetic recording medium is prepared by using the binder, the coated layer has been easily swollen by the effect of an organic solvent and it had not satisfactory temperature and humidity resistances, and the reliability for the storage of recorded data has been low whereby a high density recording could not be expected. This is serious disadvantage.